The present invention relates broadly to the manufacture of holey waveguides, to the manufacture of preforms for holey waveguides, and to the resulting holey waveguide/preform.
The term holey waveguides such as holey optical fibre used throughout the specification is intended to refer to a waveguide having a series of holes in at least a portion of the cladding material which run parallel to a guiding region. Such waveguides are sometimes also referred to as photonic crystal fibres or microstructured fibres when in optical fibre forms and the term holey waveguide is intended to include waveguides known under those various terms.
Holey waveguides such as holey optical fibres are typically fabricated by stacking tubes of uniform size into a hexagonal pattern to form a preform. One or more solid rods are inserted in the preform matrix of tubes to form waveguides, or guiding cores in the resulting optical fibre. The preform is then pulled down or drawn to a fibre of the required size. This process is sometimes repeated, or done in a number of stages.
In this production process, a very large number of tubes (e.g. greater than 100) are typically required to build up a large cladding region around the solid cores. This makes the prior art fabrication process tedious and time consuming.
While fewer layers of tubes may be used around the cores in such prior ad designs to save time and material, the resulting smaller structure, e.g. a smaller diameter optical fibre, is then difficult to use. A structure with an outer diameter close to that of e.g. a standard step index optical fibre (i.e. 125 xcexcm) is much more desirable.
In at least preferred embodiments, the present invention seeks to provide an alternative fabrication process which addresses those disadvantages of the prior art manufacturing processes.
In accordance with a fist aspect of the present invention there is provided a method of forming a holey waveguide, the method comprising the steps of forming a guiding region of a preform, forming a cladding region of the preform, wherein at least a portion of the cladding region of the preform is formed from a plurality of cladding tubes of at least two different diameters, choosing at least one of the diameters of the cladding tubes in a manner such as to reduce a total number of cladding tubes required to build up said portion of the cladding region when compared with utilising cladding tubes of the same diameter for said portion, and drawing the waveguide from the preform.
Accordingly, the number of tubes required to fabricate e.g. a holey fibre preform with a specified diameter, e.g. a xe2x80x9cstandardxe2x80x9d diameter of 125 xcexcm, can be significantly reduced.
The method may further comprise the step of choosing one or more other diameters of the cladding tubes based on a desired optical property of the optical waveguide,
The cladding tubes may be arranged in a manner such that the resulting cladding region is symmetric. The cladding region may exhibit one or a mixture of the group of square, triangular, hexagonal, octahedral and higher symmetries.
In one embodiment, the cladding tubes may be arranged in a manner such that the diameter of the cladding tubes scales with distance from the guiding region of the waveguide preform.
The core region may be formed from one or more solid rods. The one or more solid rods may be inserted into the matrix of cladding tubes to form the guiding region.
The method may comprise the step of forming a plurality of guiding regions of the preform.
The method may further comprise the step of providing one or more material members in at least one void formed by the cladding tubes. The material members may be in the form of wires of electrically and/or thermally conducting materials for poling and/or electro-optic control, and/or thermo-optic control of the waveguide.
The one or more material members may be provided in the at least one void prior to or after drawing the optical waveguide from the preform.
The waveguide is preferably drawn into a fibre form.
The method may further comprise the step of selecting the arrangement of the cladding tubes in a manner such that larger tubes are arranged near the periphery of the cladding region compared with cladding tubes near the core region, whereby irregularities in the resulting array of voids in the drawn holey waveguide due to manufacturing irregularities in tube size, and/or symmetry, and/or pressure during the drawing occur more likely at the periphery of the cladding region than near the core region.
The cladding tubes may be formed from a variety of suitable materials, including e.g. glasses and polymers.
The cladding tubes may be contained inside a containing tube for facilitating stacking of the cladding tubes and the drawing of the optical waveguide from the preform.
In accordance with a second aspect of the present invention there is provided a method of forming a holey waveguide preform, the method comprising the steps of forming a guiding region of the preform, forming a cladding region of the preform, wherein at least a portion of the cladding region of the preform from a plurality of cladding tubes of at least two different diameters, and choosing one of the diameters of the cladding tubes in a manner such as to reduce a total number of cladding tubes required to build up said portion of the cladding region when compared with utilising cladding tubes of the same diameter for said portion.
The method may further comprise the step of choosing one or more other diameters of the cladding tubes based on a desired optical property of the optical waveguide.
The cladding tubes may be arranged in a manner such that the resulting cladding region is symmetric. The cladding region may exhibit one or a mixture of the group of square, triangular, hexagonal, octahedral and higher symmetries.
In one embodiment, the cladding tubes may be arranged in a manner such that the diameter of the cladding tubes scales with distance from the guiding region of the waveguide preform.
The core region may be formed from one or more solid rods. The one or more solid rods may be inserted into the matrix of cladding tubes to form the guiding region.
The method may comprise the step of forming a plurality of guiding regions of the preform.
The cladding tubes may be contained inside a containing tube for facilitating stacking of the cladding tubes.
In accordance with a third aspect of the present invention there is provided a holey waveguide comprising a guiding region and a cladding region, wherein at least a portion of the cladding region is formed from a plurality of cladding tubes of at least two different diameters, and wherein at least one of the diameters of the cladding tubes is chosen in a manner such that a total number of cladding tubes required to build up said portion of the cladding region is reduced when compared with forming said portion from cladding tubes of the same diameter.
Preferably, the waveguide is in the form of an optical fibre.
In accordance with a fourth aspect of the present invention there is provided a preform for a holey waveguide, the preform comprising a guiding region and a cladding region, wherein at least a portion of the cladding region is formed from a plurality of cladding tubes of at least two different diameters, and wherein at least one of the diameters of the cladding tubes is chosen in a manner such that a total number of cladding tubes required to build up said portion of the cladding region is reduced when compared with forming said portion from cladding tubes of the same diameter.
Preferably, the waveguide is in the form of an optical fibre.